Samuel Howarth

Samuel Howarth
Canadian Memorial Chiropractic College | CMCC · Division of Research and Innovation

PhD (Biomechanics)

About

71
Publications
15,376
Reads
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915
Citations
Additional affiliations
June 2011 - present
Canadian Memorial Chiropractic College
Position
  • Professor (Associate), McMorland Family Research Chair in Mechanobiology
June 2011 - November 2017
Canadian Memorial Chiropractic College
Position
  • Managing Director

Publications

Publications (71)
Article
Full-text available
Background: Few studies have quantified dynamic balance in fencers despite previous suggestions that balance training may be beneficial for these athletes. Generally, asymmetry in dynamic balance performance between the left and right legs can be an indicator of lower extremity injury risk and used to monitor rehabilitation progress. Fencing is re...
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Soccer referees represent a specialized population who are required to perform decisional or perceptual tasks during physical exertion. Recent studies have demonstrated that submaximal acute exercise has a positive impact on cognitive performance. However, less is known about the impact of more strenuous exertion on cognitive performance. This stud...
Article
Objective The purpose of this study was to investigate the feasibility of measuring the immediate effects of drop-piece high-velocity, low-amplitude (DP-HVLA) manipulation to the midfoot region on jump distance in competitive adult sprinters during a standardized unilateral horizontal drop-jump (U-HDJ) test. Methods Seven asymptomatic competitive...
Article
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Background Spinal mobilization and spinal manipulation are common interventions used by manual therapists to treat musculoskeletal conditions in older adults. Their force-time characteristics applied to older adults' thoracic spine are important considerations for effectiveness and safety but remain unknown. This study aimed to describe the force-t...
Article
Objective The 5-cycle sit-to-stand (5XSTS) test is frequently used to test physical function for different clinical populations, with time to complete as the measured outcome. This study evaluated the similarity of kinematics between a single cycle of the STS movement and individual cycles of the 5XSTS test. Methods Lower extremity, pelvis, and th...
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Background Limitations in spinal mobility are a characteristic feature of Axial Spondyloarthritis. Current clinical measurements of spinal mobility have shown low criterion-concurrent validity. This study sought to evaluate criterion-concurrent validity for a clinically feasible measurement method of measuring spine mobility using tri-axial acceler...
Article
Investigating all forces exerted on the patient’s body during high-velocity, low-amplitude spinal manipulative therapy (SMT) remains fundamental to elucidate how these may contribute to SMT’s effects. Previous conflicting findings preclude our understanding of the relationship between SMT forces acting at the clinician–patient and patient–table int...
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Introduction: Manual therapy (MT) hypothetically affects discrepant neuromuscular control and movement observed in populations with low back pain (LBP). Previous studies have demonstrated the limited influence of MT on movement, predominately during range of motion (ROM) testing. It remains unclear if MT affects neuromuscular control in mobility-b...
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Background Chiropractors are a particular subset of health care professionals that reportedly suffer occupational musculoskeletal disorders (MSDs), yet they have received minimal attention to date regarding mitigating risks of occupational injury. Our study determined the prevalence of occupationally-related MSDs in the preceding year, their bodily...
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Background Understanding the mechanisms underlying chronic, nonspecific low back pain (CNSLBP) is essential to advance personalized care and identify the most appropriate intervention. Recently, two intervertebral motion biomarkers termed “Motion Sharing Inequality” (MSI) and “Motion Sharing Variability” (MSV) have been identified for CNSLBP using...
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Background: Strains of the adductor muscle group of the hip are common amongst ice hockey players. The ratio of isometric strengths between the hip adductors and abductors has been offered as a risk factor for hip adductor strain; however, there is no description for how the ratio between hip adductor and abductor strength varies as a function of h...
Article
Background: The side-bridge (SB) is a commonly used closed-chain task to assess trunk muscle endurance and side-to-side endurance asymmetry. An open-chain variation of the SB, that positions the participant in an inclined side-lying posture, may be useful for those who report shoulder pain or fatigue as the reason for terminating the closed-chain S...
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This study evaluated whether real-time applied load feedback and a predefined applied load limit improved inter-session reliability and measurement error of passive glenohumeral rotation range-of-motion measurements. Twenty-one male recreational overhead athletes completed two data collection sessions, approximately 1-week apart. Measurements of in...
Article
Spine loading data are needed to design low-back health-preserving ergonomic interventions for firefighters. Study objectives were to quantify spine loads during simulated fireground operations using simple (polynomial) and advanced (EMG-assisted musculoskeletal model) methods, and to describe the variation in spine loads between performers (N = 20...
Article
Background: Regional interdependence is conceptually based on observations that applying manual therapy to a remote anatomical region has an effect in the area of the patient's primary complaint. The current model for regional interdependence depends on force transmissibility within the body. This investigation sought to determine transmissibility...
Article
This investigation examined interactions between the magnitude of external load, movement speed and (a)symmetry of load placement on estimates of in vivo joint loading in the lumbar spine during simulated occupational lifting. Thirty-two participants with manual materials handling experience were included in the study. Three-dimensional motion data...
Article
The Turkish Get-Up (TGU) is a complex and multi-planar exercise; the performer begins in a supine lying position, progresses toward upright standing through a series of 7 stages while holding a mass overhead in one hand, and returns to the original supine lying position through a reversal of the same 7 stages. A descriptive analysis of shoulder mus...
Article
Occupations requiring prolonged periods of static standing are associated with the development of low back pain (LBP). Certain individuals are susceptible to LBP development during prolonged standing (pain developers, PDs) while others are not (non-pain developers, NPDs). Linear centre of pressure (COP) measures suggest that standing balance contro...
Article
Objectives: This investigation compared indirect 3-dimensional angular kinematics (position, velocity, and acceleration) of the lumbar spine for 2 different high-velocity, low-amplitude (HVLA) spinal manipulation procedures (lumbar spinous pull or push), and altered initial patient lower limb posture. Methods: Twenty-four participants underwent...
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Several different state-space reconstruction methods have been employed to assess the local dynamic stability (LDS) of a 3D kinematic system. One common method is to use a Euclidean norm (N) transformation of three orthogonal x, y, and z time-series' followed by the calculation of the maximum finite-time Lyapunov exponent (λmax) from the resultant...
Article
Study design: An in vivo biomechanical study. Objective: The aim of the present study was to quantify and compare the reaction loads for two spinal manipulation therapy (SMT) procedures commonly used for low back pain using a biomechanical computer model. Summary of background data: Contemporary computer-driven rigid linked-segment models (LSM...
Article
The purpose of this study was to evaluate the postural and muscular demands placed on the shoulders and neck of dental hygienists when performing a simulated manual scaling task. Nineteen healthy female dental hygienists performed 30-min of simulated manual scaling on a manikin head in a laboratory setting. Surface electromyography was used to moni...
Article
Objective: The purpose of this paper is to present the experimental setup, the development, and implementation of a new scalable model capable of efficiently handling data required to determine low back kinetics during high-velocity low-amplitude spinal manipulation (HVLA-SM). Methods: The model was implemented in Visual3D software. All contact...
Article
This investigation monitored the biomechanical demands on the lower back during simulated dental hygiene work. A total of 19 female, registered dental hygienists performed 30 continuous minutes of manual scaling (plaque removal) of a manikin's teeth while seated. We monitored the working location and orientation of the dental hygienists, with respe...
Article
The purpose of this study was to compare the spine flexion angle time histories computed with the 2 described techniques (dot product [DP] and a modified joint coordinate system [JCS] approaches) that used vector algebra and used skin-mounted markers to the spine flexion angles derived using local coordinate systems constructed from rigid bodies af...
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The mechanism of vertebral shear failure is likely a bending moment generated about the pars interarticularis by facet contact, and the moment arm length (MAL) between the centroid of facet contact and the location of pars interarticularis failure has been hypothesised to be an influential modulator of shear failure force. To quantitatively evaluat...
Article
Flexion relaxation (FR) in the low back hypothetically occurs when load is transferred from the spine's extensor musculature to its passive structures. This study investigated the influence of added upper body mass on low back kinetics and kinematics at the FR onset. Sixteen participants (8 male, 8 female) performed standing full forward spine flex...
Article
Equations used to determine vertebral failure tolerances without the need for destructive testing are useful for scaling applied sub-maximal forces during in vitro repetitive loading studies. However, existing equations that use vertebral bone density and morphology for calculating compressive failure tolerance are unsuitable for calculating verteb...
Article
Segmental instability, characterized by excessive or aberrant movement of the vertebrae can be assessed quantitatively using mechanical characteristics within a region of minimal resistance called the neutral zone. The diagnosis of instability is often used to decide whether or not to surgically fuse the vertebrae. Alterations in flexion/extension...
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In most genuine industrial settings, it is not yet feasible to directly measure in vivo tissue loads, nor is it practical to estimate dynamic load-time histories using biomechanical models. Thus, data extrapolation techniques are often used for obtaining occupational estimates of shift or daily cumulative low-back load exposures. These techniques a...
Article
The transverse carpal ligament (TCL) influences carpal stability and carpal tunnel mechanics, yet little is known about its mechanical properties. We investigated the tissue properties of TCLs extracted from eight cadaver arms and divided into six tissue samples from the distal radial, distal middle, distal ulnar, proximal radial, proximal middle,...
Article
An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to submaximal cyclic or static compressive forces while in a flexed, neutral, or extended posture. To investigate the combined effect of cyclically applied compressive force (e.g., vibration) and postural deviation on intervertebral joint mechanics. Independently...
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Despite the findings that peak anterior shear load is highly correlated with low-back pain reporting, very little research has been conducted to determine how vertebral shear injury potential is influenced. The current study quantified the combined effects of vertebral joint compression and flexion/extension postural deviation from neutral on ultim...
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The goal of the current investigation was to propose and evaluate a method for estimating cumulative spinal loading based on the hypothesis that cumulative loading for a single task will be linearly proportional to its cycle time. The association between cumulative spinal loading and low-back pain has driven ergonomists and researchers to develop n...
Article
This study investigated the effects of loading and posture on mechanical properties of the transverse carpal ligament (TCL). Ten fresh-frozen cadaver arms were dissected to expose the TCL and positioned in the load frame of a servo-hydraulic testing machine, equipped with a load cell and custom made indenters. Four cylindrical indenters (5, 10, 20,...
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Vertebral joint fatigue life non-linearly decreases with increasing anterior shear force magnitude. Therefore, equal treatment of independent shear force exposures will underestimate low-back injury potential. This investigation developed mathematical functions for deriving appropriate weighting factors (WFs) to be applied in occupational cumulativ...
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Marker obstruction during human movement analyses requires interpolation to reconstruct missing kinematic data. This investigation quantifies errors associated with three interpolation techniques and varying interpolated durations. Right ulnar styloid kinematics from 13 participants performing manual wheelchair ramp ascent were reconstructed using...
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Estimates of cumulative load are typically based on a direct integration of instantaneous compressive loads. Recent evidence suggests that higher loads as well as smaller rest to work durations should receive greater importance in the calculation of cumulative compressive load, especially if insight into potential injury mechanisms is sought. The p...
Article
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Prolonged occupational standing has previously been associated with low back pain (LBP) development. The immediate effects of a bout of prolonged standing on subsequent functional movement performance have not been investigated. It is possible that including a period of prolonged standing may have acute, detrimental effects. The purpose of the stud...
Article
While the individual tissues of the vertebral joint demonstrate viscoelastic properties, the global viscoelastic properties of the lumbar vertebral joint are not well established. This study investigated how changes in displacement rate influenced the mechanical response of the porcine cervical spine (a surrogate or model for the human lumbar spine...
Article
To quantify levels of torso muscular demand during wheelchair ramp ascent and the ability of a geared wheel to influence trunk muscle activity. Repeated-measures design. Each participant completed manual wheelchair ramp ascents for each combination of 4 ramp grades (1:12, 1:10, 1:8, and 1:6) and 3 wheel conditions (in gear, out of gear, and a stand...
Article
Shoulder muscle overuse has been linked to the high prevalence of shoulder injuries in manual wheelchair users. Ramp ascent is a barrier that is often faced by manual wheelchair users that requires higher muscle activations than level wheelchair propulsion. Additionally, reported subjective measures of shoulder pain are reduced amongst manual wheel...
Article
To determine the utility of the active straight leg raise (ASLR) test as a screen of lumbar spine stability and abdominal bracing (AB) ability. A biomechanical study of the ASLR test as a clinical evaluation of lumbar spine stability and AB. Clinical research laboratory. Fourteen participants who were currently asymptomatic for back pain and leg pa...
Article
Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering e...
Article
Technical note. To provide background theory and information and to describe relevant applications of autocorrelation and cross-correlation methodology as they apply to the field of motor control in human movement and rehabilitation research. Commonly used methodologies for pattern and event recognition, determination of muscle activation timing fo...
Article
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The ProFitter 3-D Cross Trainer is a labile surface device used in the clinic and claimed to train spine stability. The purpose of this study was to quantify the spine mechanics (compression and shear forces and stability), together with muscle activation mechanics (surface electromyography) of the torso and hip, during three ProFitter exercises. T...
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The purpose of this study was to determine the effect of a fatiguing task (3 min intense stair climbing) on the adopted spinal postures and trunk muscular activation patterns during three highly physically demanding simulated firefighting tasks. Following the fatigue protocol, it was observed that individuals adopted significantly greater spinal fl...
Article
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The goal of this study was to quantify the relative contributions of each muscle group surrounding the spine to vertebral joint rotational stiffness (VJRS) during the push-up exercise. Upper-body kinematics, three-dimensional hand forces and lumbar spine postures, and 14 channels (bilaterally from rectus abdominis, external oblique, internal obliqu...
Article
The influence of signal sampling frequency and the low-pass digital filter cutoff frequency on the minimum number of padding points when applied to kinematic data are factors often absent in data processing descriptions. This investigation determined a relationship between the number of padding points and the ratio of filter cutoff to signal sampli...
Article
Push-up exercises are normally performed to challenge muscles that span upper extremity joints. However, it is also recognized that push-ups provide an effective abdominal muscle challenge, especially when the hands are in contact with a labile support surface. The purpose of this study was to compare trunk muscle activation levels and resultant in...
Article
Quantifying the stability of the spinal column offers a perspective on the effectiveness of the motor control strategy to ensure a stable spine--and minimize the risk of injury from experiencing an unstable event. There are essentially three energy based methods of calculating a stability index for the lumbar spine. All three methods involve mathem...

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